Field of the Invention
This invention is related to the field of power management in integrated circuits.
Description of the Related Art
A given integrated circuit can include a variety of components, and in some cases multiple instances of the same component. For example, a system on a chip (SOC) can include one or more processors forming the central processing units (CPUs) of the SOC, one or more memory controllers, various peripheral circuits such as graphics devices, display controllers, image processing components, audio processing components, networking components, peripheral interface controllers, etc. Each component is designed to operate at a specified clock frequency (or, more briefly, frequency) and a corresponding power supply voltage magnitude. Different components can have different operating points (frequency/power supply voltage magnitude pairs), and if the voltage magnitudes differ during use there can be different power supply voltage planes in the integrated circuit.
The actual power supply voltage magnitude supplied to the component during use is greater than the power supply voltage magnitude for which the component is designed. A significant portion of the difference (referred to as the voltage margin, or simply margin) accounts for potential voltage loss (referred to as voltage drop or droop). Particularly, significant sources of power supply voltage variation during use are current-resistance (IR) drop due to resistance between the power management unit that supplies power to the integrated circuit and the loads within the integrated circuit. The resistance can include resistance in the conductors on the board, resistance in the conductors between the pins of the integrated circuit package and the loads within the integrated circuit (e.g. the components of the integrated circuit), etc. The greater the current drawn by the component, the higher the IR drop. Additionally, significant changes in the current causes transient voltage droop (referred to as L*di/dt voltage droop, as the combination of inductance in the system and the transient current changes cause the droop). In order to ensure that components operate properly under all conditions, the worst-case current and di/dt conditions are assumed for the component and the required power supply voltage magnitude is increased to ensure that even if the worst-case conditions are occurring, the power supply voltage magnitude experienced by the component is sufficient for correct operation. When multiple instances of a component are included (e.g. multiple processors), all of the instances are assumed to operate at worst-case concurrently and a corresponding voltage margin is determined.
Maintaining a higher power supply voltage magnitude than otherwise required sacrifices power and high end performance. The IR drop and L*di/dt droop are highly workload dependent, varying with the number of instances that are active and whether the workload is utilizing the most power intensive portions of the instances. Thus, at times in which the instances are not presenting worst-case loads to the power supply, the voltage margin is larger than required and power consumption is higher than necessary.